Labeling chemistry is generally used to improve a mass spectrometry signal.
Conjugation using an aqueous ene-type reaction to derivatize tyrosine using the reagent 4-phenyl-3H-1,2,4-triazole-3,5(4H)-dione (commonly known as PTAD or Cookson Reagent) can provide a particularly useful conjugate for the synthesis of bispecific antibodies (Hitoshi Ban, Jilia Gavrilyuk, Carlos F. Barbas, J. Am. Chem. Soc. 2010, 132, 1523-1525). PTAD has also been used for conjugation with Vitamin D class of compounds for mass spectrometry analysis (Kazutake Shimada, Tomoyuki Oe, Tatsuhito Mizuguchi, Analyst, 1991, 116, 1393-1397).
Quaternary amino oxy Cookson (“QAOC”), a reagent having the same reactive core as PTAD, was developed for the analysis of Vitamin D3 metabolites, as described in U.S. Pub. Pat. Appl. 2011/0212534, which is incorporated by reference herein in its entirety. This reagent was found to react with the conjugated diene functionalities of Vitamin D3 to provide improved ionizing and fragmentation properties for mass spectrometry (MS) analysis of Vitamin D3.
The accurate analysis and quantification of hormones and other compounds containing phenolic OH is becoming increasingly important. For example, estrogen and estrogen-like compounds are playing an ever-increasing role in today's society through hormone replacement therapy. Also, the analysis and quantification of estrogen and estrogen-like compounds helps in the management of estrogen-related diseases, like breast cancer.
However, a need still exists for labels for improved mass spectrometry analysis of compounds containing phenolic OH, such as steroids or estrogens. Analysis of these compounds, which can include hormones such as estradiol, by mass spectrometry has conventionally been difficult. For example, many of these compounds do not contain ionizable groups. Thus, the quantitation of these molecules, e.g. estradiol, in a biological matrix, especially at low concentrations, can be difficult.
While reagents such as pentafluorobenzylbromide and dansyl chloride are commonly used in derivatization strategies for estradiol analysis using mass spectrometry, current strategies involving LC/MSMS for exploiting such derivatization of analytes containing phenolic OH fails to achieve the limit of detection required for clinical assays (Shimada, et.al., Analyst, 116, 1393-1397 (1991); Higashi et al., Chem. Pharm. Bull., 54(11), 1479-1485 (2006)). A need exists for a method of quantitating these analytes that overcomes these drawbacks.